Yes, radius is a Scrabble word!

Noun

1. The length of a line segment between the center and circumference of a circle or sphere

2. A straight line from the center to the perimeter of a circle (or from the center to the surface of a sphere)

3. A circular region whose area is indicated by the length of its radius

4. The outer and slightly shorter of the two bones of the human forearm

5. Support consisting of a radial member of a wheel joining the hub to the rim